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On Fri, Nov 12, 2021 at 6:04 PM Patricio A. Greco via groups.io

<patricio_greco@...> wrote:

That’s correct this is a como failure on that analyzers.
Try to perform adjustments tasks on synthesizers ( samplers … and so) if
it don’t fix the problem you will need a new oscillator .

Thanks Patricio. Given that the problem occurs well before the synthesizers
in the signal chain I'm going to go ahead and chalk this one up to a bad
YTO. Unfortunate, but at least I didn't pay much for this 8593E.

Does anyone on the list have recommendations for YTO diagnosis and rebuild,
especially since it seems Luis Cupido is no longer offering this service?
Test-Cal Instruments on eBay purports to be able to rebuild them; does
anyone have experience with them?

Thanks,
Nick

Ing. Patricio A. Greco
Taller Aeronáutico de Reparación 1B-349
Organización de Mantenimiento Aeronáutico de la Defensa OMAD-001
Gral. Martín Rodríguez 2159
San Miguel (1663)
Buenos Aires
T: +5411-4455-2557
F: +5411-4032-0072
www.servicios-electronicos.com

On 12 Nov 2021, at 19:39, Nick Foster <bistromath@...> wrote:

?
Hi all,

Hi all,

I'm working on the old 8593E I picked up off eBay a few years back. It had
the problem when I got it -- I figure the seller probably knew and didn't
mention it, but *caveat emptor* and all that.

The problem manifests as extreme, sporadic phase noise. Like this:
[image: image.png]

That's a relatively tame example, and occasionally it will wipe out the
whole trace. It's all FM noise.

I spent a while digging around the analog interface board and it seems to
be OK. One thing I noticed is that the FM coil drive diagnostic screen
(measuring FM+) shows a flat line. That said, the analyzer sweeps just
fine
below 10MHz spans where the FM coil is active (albeit with noise), and a
scope does show some low voltage on that (current-driven) coil line, so I
think it's probably OK (given the FM coil R is 1.25 ohms with <150mA, how
did the FM coil diag measurement ever hope to show it on the trace?). The
noise didn't change when I disconnected the A25 counter/lock assembly.

I disconnected the FM coil drive and ran the YTO's output after the
isolator into another spec an, and it shows the YTO exhibiting exactly the
same noise. I don't have a current source on hand which is quiet enough to
drive the main coil and really rule out the main coil driver on the analog
board. The YTO seems to sweep OK across its range with good power (~+12dBm
after the isolator and directional coupler).

Before I get too deep in the rabbit hole building a quiet current source,
is this behavior a known symptom of YTO failure on the 859xE? What are the
odds this could be noise in the main coil driver or +15/-15/+5 power
supplies to the YTO? They seem clean to my scope, but it's very difficult
to get good mV/uV-level noise measurements. If it is the YTO, does it seem
likely to be the dreaded wirebonded transistor, or the circuitry on the
control board?

Nick